Devices used for the inspection of internal spaces are configured to move automotively, without the aid of movement from another source or human being. They contain actuators or motors for the movement of wheels, legs, or caterpillars, which advance the device along a surface. In order to allow the inspection of the entire internal space the devices are equipped such that they can remain in contact with all surfaces, including sidewall and ceiling surfaces. In the case of ferromagnetic surfaces as for example in machines, turbines, or motors, such devices are equipped with permanent magnets or electromagnets incorporated into the legs, wheels, or caterpillars. The magnets allow movement of the inspection device along very steep or vertical walls as well as when it is upside down.
Automotive devices for inspection of internal spaces are dimensioned according to the size of an opening provided to enter the internal space to be inspected. In particular, the size of legs, caterpillar or diameter of wheels and the motor for advancing the device are limited according to the opening. The devices are accordingly suitable for the inspection of flat and convex surfaces as well as surfaces having concave contours that are large compared to the size of the legs, wheels, or caterpillars. If the contour of the surface however, is more complex and includes piping, steps, holes, or grooves, as for example in steam turbine parts such as steam chests, then advancing a device along the surfaces becomes more complex. In particular, when concave contours are smaller than the size of the wheels or caterpillars, the device is no longer able to advance as illustrated for example in FIG. 1. FIG. 1 shows wheels of an inspection device equipped with wheels 3 with magnets providing contact with a ferromagnetic surface 4 at all times. The wheels 3 of the device have reached a concave step of the surface 4, where the step height is smaller than the wheel diameter. The wheel is in contact at two points of the surface, the magnetic forces acting at both points. The motor is not strong enough to overcome the magnetic forces and cannot advance the device any further along the surface.